Ring roller mill

ABSTRACT

A ring roller mill for grinding mineral clinker materials and the like comprises at least one grinding ring, at least one roller and at least one air outlet opening within the outer circumference of the grinding ring and air inlet openings on each side of the air outlet opening in the rotating direction of the grinding ring. The location of the air inlet and outlet openings, and respectively, relative to each other ensure that substantially lower flow rates occur in the mill at a certain volume flow rate compared to hitherto known mills. At the same time a more stable operation of the mill is ensured.

BACKGROUND OF THE INVENTION

The invention relates to a ring roller mill for grinding mineral clinkermaterials or the like and comprising at least one grinding ring and atleast one roller as well as air inlet and air outlet openings for thepassage of air.

Such mills may for example be used in connection with the production ofcement where cement, slags or the like receive final grinding.

Compared to other roller grinding apparatuses, a ring roller mill ischaracterized in that the recycling of material may be effected insidethe mill as it is also seen in e.g. a tube mill. However, it is adisadvantage of a tube mill that it is significantly morespace-consuming than a ring roller mill of identical capacity.

Ring roller mills with and without air passage are commonly known, andthe separation of finely ground material may for instance be effected byconveying a portion of the ground material to a sieve where materialhaving a certain defined maximum grain size is separated off whereas theremaining material is recycled. Thus, material is recycled whichcomprises so small grains that, in such mills, operation problems in theform of vibrations often occur during fine-grinding.

In case of ring roller mills of the type disclosed above which are knownfrom i.a. DE patent No. 667,011 and from U.S. Pat. No. 1,693,247, theair is caused to pass through the milling chamber along one singleroute, usually axially in the mill, which means that operation takesplace at high air flow rates with ensuing losses of pressure in thevolume flow rate of air which is necessary for the conveyance of theground material out of the mills. Consequently the establishment of suchair flow requires much power. Moreover, the large flow velocity meansthat particles having substantially larger grain sizes than desired aredischarged from the mill. Therefore, such particles Bust be separatedoff and reconveyed to the mill. The known mills are associated with theadditional disadvantage that a unilateral passage of air effects anaccumulation of material at the one side of the mill thereby causinglop-sided operation with ensuing increased loads on roller, grindingring, bearings, etc. Said disadvantages associated with the known ringroller mill, viz. a large power consumption and the necessarycomprehensive reconveyance of material from a separation process to themill, mean that, despite the disadvantages associated therewith, it hasbeen preferred to use the tube mill rather than ring roller mills.

SUMMARY OF THE INVENTION

Therefore, it is the object of the invention to provide a ring rollermill of the type disclosed above which requires substantially lesspower, provides improved material distrubution in the mill, and whereinreconveyance of separated material is reduced.

This object is achieved with a ring roller mill which is characterizedin that it comprises at least one air outlet opening provided within theouter circumference of the ring and at least one air inlet opening ateach side of said air outlet opening in the rotating direction of thering.

As the inlet openings are located at each their side of the outletopening and the air passages between the inlet and the outlet openingsdo not have common flow routes until they meet at the outlet, the flowrate at each side of the outlet opening may be reduced substantiallycompared to the flow rate in a Bill where the entire flow of air iscaused to follow one single flow route, and consequently the pressureloss across the mill may be reduced significantly. The reduced flow ratemoreover means that the power exerted on the particles in the millingchamber is reduced thereby preventing larger particles than intendedfrom being carried along with the air flow and thus eliminating the needfor comprehensive reconveyance of material to the mill.

According to a preferred embodiment the ring roller mill according tothe invention may be provided with an outlet opening on each side of thegrinding ring and with inlet openings located at each side of the outletopenings and at both sides of the grinding ring. This has the additionaleffect that the air flow becomes symmetrical about a plane perpendicularto the rotating axis of the ring and the said accumulation of materialeat the one side of the mill is avoided.

In both cases a mill of compact construction is obtained which millrequires a low energy consumption as well a limited reconveyance ofmaterial thereby making the ring roller mill according to the inventionparticularly desirable compared to other mill types, such as the tubemill.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the invention will be explained in the following withreference to the drawings, wherein

FIG. 1 is an axially sectional and schematical view of a ring rollermill,

FIG. 2 is a diametrally sectional and schematical view of a ring rollermill, and

FIG. 3 is a view of a ring roller mill seen from above.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the embodiment shown the mill is provided with a grinding ring 1 anda roller 2. By means of a shaft the roller is connected to a motor (notshown). The ring is also rotated by means of a driving mechanism (notshown). The grinding ring and the roller are encased so that undesirableescape of ground matter from the grinding chamber does not occur. Thering roller mill is provided with air inlet openings 5a, 5b, 6a, 6b andair outlet openings 3, 4 in the casing and on each side of the ring. Thelocations of the openings, except for the opening 6b, will appear fromFIGS. 1 and 2. The not shown air inlet opening 6b is located oppositethe opening 5b.

It will appear from FIG. 2 that the air inlet openings are located ateach their side of the outlet opening in the rotating direction of thering.

In communication with the air inlet openings 5a, 5b, 6a, 6b ducts 11a,11b; 7a, 7b are arranged. The air outlet openings 3, 4 arecorrespondingly provided with ducts 8, 10.

In communication with an air inlet opening a duct 9 is arranged for theintroduction of new material and for recycled material.

The conveyance of finished material away from the mill is effected by avolume flow of air therethrough which is adjusted in accordance with thegrinding capacity of the mill.

During operation the air flows between the inlet openings 5a, 5b, 6a, 6band the outlet openings 3, 4 will thus be separate until they meet atthe outlet openings. Hereby it is obtained that the volume flow isdivided so as to follow separate flow routes. The flow rate is reducedwith a value which corresponds to the distribution of the volume flow,preferably in a 1:1 ratio on each side of the outlet openings. Thepressure loss in a duct flow will depend on the square of the flow rate,and a 50 per cent reduction of the flow rate thus reduces the pressureloss to one fourth.

Symmetrically located inlet and outlet openings provides evendistribution of the material in the mill and the lopsided operation ofthe roller and the grinding ring with ensuing mechanical loads and wearis avoided.

Moreover, the use of two outlet openings makes it possible to coupleseparators with different characteristics to each pipeline 8, 10 therebypermitting a more flattened distribution of the cement grain size.

I claim:
 1. A ring roller mill comprising at least one grinding ring andat least one roller as well as air inlet and outlet openings,characterized in that the mill comprises at least one air outlet openingprovided within the outer circumference of the grinding ring and atleast one air inlet opening provided on each side of the air outletopening in the rotating direction of the grinding ring.
 2. A ring rollermill according to claim 1, characterized in that air outlet openings areprovided on each side of the grinding ring, and that air inlet openingsare provided on each side of the two air outlet openings.
 3. A ringroller mill according to claim 2, characterized in that the individualair outlet opening is provided in an area above the roller where thedistance between the grinding ring and the roller is the largest, andthat the air inlet openings are arranged symmetrically relative to eachoutlet opening.
 4. A ring roller mill according to claim 1,characterized in that the individual air outlet opening is provided inan area above the roller where the distance between the grinding ringand the roller is the largest, and that the air inlet openings arearranged symmetrically relative to each outlet opening.